Abstract Background Amaranthus palmeri has emerged as the most widespread weed of agricultural land in large parts of North and South America. Understanding its population dynamics and the influence of meteorological variables becomes important for decision-making in an integrated management context. The hypothesis is that the emergence of A. palmeri is influenced by thermal time and extreme weather events that occurred in the previous 45, 30 or 15 days. Objective The work was aimed to detect the influence of meteorological variables and extreme weather events on the emergence of A. palmeri under field conditions. Methods A field experiment was carried out in order to record seedling emergence of A. palmeri in two growing seasons, 2017/2018 (S1) and 2018/2019 (S2), in Argentina. Associations between weed emergence and thermal time (in growing degree-days GDD), meteorological variables or extreme weather events recorded at 15, 30 and 45 days before to each evaluation time were studied by regression, principal components and multiple correspondence analyses. Results Thermal time was closely associated to the progress of cumulative emergence in both seasons, but the emergence periodicity was conditional with rainfall. The high precipitation during the spring determined a short lag period (121.8 GDD) in S2. Contrarily, the largest lag period (236.6 GDD) was detected in S1 related to a drought that concentrated the emergence in the beginning of the summer when the rainfall increased. Conclusions Thermal time allows the cumulative emergence prediction; however, extreme weather events like drought induce quiescence, concentrating the emergence in a short period.

SUMMARY The atrazine molecule in the soil is degraded by chemical and microbiological processes, depending on the physicochemical, biological properties of the substance and on meteorological factors such as temperature and humidity. The objective was to evaluate the time of degradation and the presence of metabolites in contrasting agricultural managements during a period after application. The work was carried out in a field trial and we could see that in a period less than 30 days the concentration of atrazine was reduced by 90% in the first 5 cm of depth.

RESUMEN La molécula de atrazina en el suelo se degrada mediante procesos químicos y microbiológicos, dependiendo de las propiedades físico-químicas, biológicas del suelo y de factores meteorológicos como temperatura y humedad. El objetivo fue evaluar el tiempo de degradación y presencia de metabolitos en dos manejos agrícolas contrastantes durante un periodo de tiempo posterior a la aplicación. El trabajo se realizó en un ensayo de campo y pudimos observar que en un periodo menor a 30 días la concentración de atrazina se redujo en un 90% en los primeros 5 cm de profundidad.